The invention concerns a miniature microphone assembly advantageously based on silicon technology which can preferentially be manufactured using micromechanical methods.
Microphones transform sound into electrical signals. Certain applications require a reduction in the size of a microphone, for example for use in hearing aids. However, a reduction in the size of the microphone often leads to a reduction in the size of the microphone signal due to an associated reduction in the size of the sound-detecting diaphragm. The miniaturization of microphones based on silicon technology has been effected with the assistance of micromechanical techniques. Towards this end it has been possible to reduce the size of microphone membranes to less than 1 mm.sup.2. The sensitivity of such microphones is typically less than 1 mV/Pa. Current techniques allow for simultaneous manufacture of the microphones and integrated circuits on the same chip in order to be able to amplify the small signal directly at the location of signal production to thereby improve the signal-to-noise ratio. All microphones using this technology of prior art utilize a microphone membrane aligned perpendicular to the incident direction of the sound for maximizing the microphone sensitivity.
This technology has the disadvantage that, despite utilization of silicon chip technology, the chip area cannot be made as small as possible since signals of insufficient strength would thereby result for membrane sizes under 1 mm.sup.2. In addition, the membrane is surrounded by a frame needed for membrane support and the electronic amplification circuit requires additional surface area to be accommodated within this frame so that the microphone surface which is actually available for sound purposes cannot be less than several mm.sup.2 in size.
Departing from this prior art, it is a primary object of the present invention to improve this arrangement for miniaturized microphone assemblies based, in particular, on silicon technology to overcome the problems associated with large external frontal areas while nevertheless maintaining a good signal-to-noise ratio for the microphone and a compact overall size.